In an electromechanical watch, the hands are generally driven via a gear set or train, which may be actuated by a Lavet stepping motor. In that case, the hands are driven in steps by one or two wheels of the gear train by actuating the stepping motor. A significant positioning torque on the stepping motor means that time indicator hands with a high level of unbalance can be used. These hands may be larger or heavier. When there is a shock to the watch, the positioning torque of the electric motor can hold the hands in position, but there may be a time-lag in said time-indicator hands, which is a drawback of a state of the art electromechanical watch.
It is also to be noted that if the positioning torque becomes too high, the electric motor can no longer rotate, which is also a drawback. It is then necessary to optimise the electric motor as far as possible, but this inevitably also leads to an increase in the electrical power consumption required to drive hands with a high level of unbalance. This is undesirable when the watch is powered by a cell or battery.
CH Patent Application No. 699 771 A2, which discloses a locking device for a toothed wheel of a timepiece module, may be cited. The toothed wheel is driven by a click actuated by a Lavet stepping motor. Between each actuation of the motor, at least one guided finger is housed between two teeth of the toothed wheel to lock the wheel. The finger is driven into a locking position by an electrostatic actuator. However, the arrangement of locking the toothed wheel between each actuation of the electric motor is relatively complicated, which is a drawback.